This invention relates to the preparation of 2-keto-L-gulonic acid by microbiological means.
2-keto-L-gulonic acid is a valuable intermediate in the preparation of ascorbic acid (vitamin C), an essential vitamin for human nutrition. Processes for converting 2-keto-L-gulonic acid to ascorbic acid, for example by heating in the presence of a base, are well known in the art.
Only a limited number of microorganisms are known in the art to be effective for the reduction of 2,5-diketo-D-gluconic acid to form 2-keto-L-gulonic acid, as shown for example in U.S. Pat. Nos. 3,963,574, 3,922,194 and 3,959,076. Microorganisms of the genus Citrobacter have not previously been disclosed to be effective in this reaction.